If you happen upon some larvae (or by this late in the spring, tadpoles) don't interrupt the process. (Check your local & state laws.) But if you see some danger to them, you could try to raise them. Giulia's editor raised three tadpoles to froghood some years back. They looked much like the teeny frog in the photo. They also had cute stripey legs that were très chic, honestly. (But that's not why they were adopted...catching all those insects was a total pain: you've been warned.) When they grew up, they were returned to their native area.